Pulse analyzing



June 4, 1963 c. M. CLARK 3,092,751

PULSE ANALYZING Original Filed June 28, 1957 5 Sheets-Sheet 1 PULSEPULSE ta COUNTER GENERATOR 11 43 T K; PULSE sI-IAPER DIFFER. CIRCUIT 1 24 N I r DEPTH LINEAR SWEEP INDICATOR GENERATOR '7 r T READ OUT FEED BACKRECORDER AMPLIFIER 2 T r READ OUT AMPLIFIER f--- TIME MODULATED IT: IPULSE GENER. 32 t l AMPLITUDE :lm COMPARATOR ,4

I LINEAR SWEEP 42 GENERATOR l READ I .3/

PULSE sTRETcI-IER I r I GATE DISCR. GENER- INVENTOR CALVIN M. CL K [d Aam- TORNEYS CLARK PULSE ANALYZING June 1963 5 sheeizsns 2 Original FiledJune 28, 1957 DEPTH INDICATOR PULSE GENERATOR READ OU AMPLIFIER DRECORDER PULSE SHAPER GENERATOR SWEEP ERATOR (WRITE) Fl G. 2

NVENTOR ALV/N M. CLARK BY 24$ a W TORNEYS June 4, 1963 C. M. CLARKOriginal Filed June 28, 1957 PULSE ANALYZING 5 Sheets-Sheet 3 4s 55 5/K- K- PULSE DEPTH RECORDER SHAPER I INDICATOR PULSE 5.2 GENERATOR mVIDEO v AMPLIFIER M v M b MONITOR SLOW a swITcI-I swEEP I GENERATOR v saI I FAST M swEEP GENERATOR W HM ,205 WRITE b READ a wRITE a I I I 206READ b 202 i 204 I I Ow PASS FILTER v I I VIDEO -48a AMPLIFIER HlvINVENTOR CALV/N M. CLARK BY z A M [d A ORNEYS C. M. CLARK PULSEANALYZING June 4, 1963 5 Sheets-Sheet 4 Original Filed June 28, 1957 N9NS JAAA AAAA

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5 Sheets-Sheet 5 C. M. CLARK PULSE ANALYZING TO TIME MODULATED PULSEGENERATOR INVENTOR CALVIN M. CLARK BY Q 2 [(1. MM A ORNEYS FROM PULSESTRETCHER FIG. 5

June 4, 1963 Original Filed June 28, 1957 United States Patent 3,092,751PULSE ANALYZING Calvin M. Ciark, Fullerton, Calif, assignor toCalifornia Research Corporation, San Francisco, Calif., 21 corporationof Delaware Original application lune 28, 1957, Ser. No. 668,781, newPatent No. 2,968,724, dated Jan. 17, 1961. Divided and this applicationSept. 28, 1959, Ser. No. 842,622

2 laims. (Ci. SIS-8.5)

This invention relates to a method of and apparatus for analyzing theamplitude distribution of electrical Waveforms and more particularly amethod of and apparatus for converting varying amplitude high-frequencyintelligence to time modulated signals, transmitting said signals alonga well logging cable of limited frequency and power't'ransmissioncharacteristics, storing said sigrials as discrete segments of circulartraces on the storage surface of a cathode-ray storage tube inpredetermined locations in accordance with the varying amplitudes of theoriginal high-frequency intelligence and reading from the storagesurface the information stored thereon after a predetermined quantity ofintelligence has been accumulated for reproduction in a spectrographicform. This application is a division of my copending application SerialNo. 668,781, filed June 28, 1957 now Patent No. 2,968,724, dated January17, 1961 for Pulse Height Analyzer.

In logging of earth formations traversed by a well bore it is frequentlydesirable to be able to transmit high-frequency forms of intelligence,such as electrical pulses representing gamma ray energies which are ofvery short duration and very rapidly succeeding each other, over acableof relatively limited frequency and power transmissioncharacteristics. In particular, it is highly desirable to be able totransmit the electrical pulses corresponding to the individual 'y raysgenerated instantaneously upon interaction of neutrons with nuclei ofconstituent elements of an earth formation lying several thousand feetbelow the earths surface. However, this desire has been found sodifficult that the solutions suggested for field practice heretoforehave required either that the recording be performed blind, by meanssuch as camera and film within the well bore adjacent the logging tool,or that the signal be transmitted over cornmercially unavailable coaxialcables. As particularly explained in'the' copending application ofDelmar O. Seevers, Serial No. 433,244, filed May 28, 1954, which isassigned to the assignee of the present application, these previouslyknown methods of transmitting high-frequency forms of intelligence havebeen considered so unattractive that they have retarded or prevented thefield use of spectral analysis of earth formations by means of y rayenergies. As further explained in the said Seevers application, theintelligence originating in high-frequency form may be transmitted overa standard well logging cable of limited frequency and powertransmission characteristics by conversion of the electrical pulses,corresponding to the individual energy of each "y ray detected by ascintillation crystal and photomultiplier tube combination, to anelectrostatic charge in a cathode-ray tube having an electrostaticcharge modifiable storage surface, then assigning a particular locationor position on the storage surface for storage of said charges or pulsesin accordance with the energy of each "y ray and subsequently readingout the stored information for transmission in low-frequency form.

In my copending application, Serial No. 451,525, for Circular ScanningSystem for Recording Nuclear Energy Spectrum, filed August 23, 1954 andassigned to the same assignee as the present application, the advantagesprovided by polar coordinate storage of the ray spectrum ice have beendescribed. The system of my copending application employs anelectrostatic deflection type cathoderay storage tube. The polarcoordinate storage system of that application requires the conversion ofthe intelligence into its sine-cosine coordinates to produce the polarcoordinate deflection pattern on the storage surface of the storagetube.

Present commercially avaflable electromagnetic deflection typecathode-ray storage tubes provide substantially improved resolution overthe best electrostatic tubes. The improved resolution increases thestorage capacity of the tube by the square of the resolution improvementdue to the polar type distribution of the information on the storagesurface, thus providing a much more desirable and efficient storagedevice.

The present application discloses a system employing a cathode-raystorage tube with electromagnetic deflection for positioning theintelligence on the storage surface of the tube in which deflectingfiield is rota-ted about the axis of the storage tube to eifect theangular rotation of the electron beam of the tube. The intelligence ispositioned at varying distances along a radius of the circular scanningpattern of the storage tube in accordance with the energy of theinformation and is disposed along a circular path as a discrete portionof a trace in accordance with the angular position of the deflectionfield at the time of recording. Recording of the intelligence iscontinued in the manner just defined until a predetermined quantity ofintelligence counts has been attained or until a selected area of a wellbore has been surveyed at which time the intelligence so stored isremoved from the storage surface of the tube. This readout may beaccomplished in any suitable manner, one of which includes the sweepingof the storage surface in a spiral manner about the center of the storedinformation as an axis. The readout procedure is continued until all ofthe intelligence stored on the face of the tube has been read and anindication of this intelligence has been recorded. The readou proceduremay also include an erasing process as the intelligence is read or thestorage surface may be erased in a subsequent operation to be returnedto a condition for subsequent intelligence storage.

An object of the present invention is an improved method forintelligence disposition on the storage surface of a cathode-ray storagetube.

A further object of the present invention in accordance with thepreceding object is a method for analyzing the amplitude distribution ofelectrical wave-forms employing a cathode-ray storage tube having arotating magnetic deflection system whereby time modulated intelligencederived from the electrical Waveforms may be fed directly to thedeflection system and storage tube for disposition in accordance withthe amplitude distribution thereof.

Another object of the present invention is an electronic circuitarrangement for converting high-frequency intel ligence information totime modulated signals for transmission over a cable of limitedfrequency and power transmission characteristics.

A further object of the present invention in accordance with thepreceding object is a well logging system having part of its componentsWithin the Well bore and part of its components at the surface of theearth formation being logged with the components within the well boreincluding electronic circuitry for converting intelligence signals ofhigh-frequency characteristic to time modulated signals for transmissionalong a well logging cable to the components at the earths surface fordisposition at that point.

A further object of the present invention is an improved energizationand control system for a cathode-ray storage tube wherein intelligenceinformation is stored on the tube upon the occurrence of coincidencebetween a voltage of predetermined characteristic and a voltageproportional to said intelligence information.

Further objects and featuresof the invention Will be readily apparent tothose skilled in the art from the specification and appended drawingsillustrating certain preferred embodiments in which:

FIG. 1 is a schematic representation of the logging tool as well as thetransmitting and recording equipment incorporating the method of thepresent invention as applies to the logging of 'y ray energy spectra.

FIG. 2 is a schematic representation of the recording equipmentincorporating the method of the present invention and illustrating themanner of positioning the electrostatic charges on the storage surfaceof the storage tube as contemplated during the Writing operation, of thelogging procedure.

FIG. 3 is a schematic representation of a continuously operable welllogging system incorporating the method of the present invention.

FIG. 4 is a schematic circuit diagram of the pulse stretcher of thepresent invention.

FIG. 5 is a schematic circuit diagram of the amplitude comparator of thepresent invention.

Referring now to the drawings, and in particular to FIG. 1, there isillustrated a preferred form of apparatus adapted to utilize the methodof transmitting intelligence originating in high-frequency form over awell logging cable 11 of limited frequency and power transmissioncharacteristics. As shown, a logging sonde 12, wherein the earthformation analysis and signal generating equipment are located, isadapted to traverse a well bore 13 while supported on the lower end ofthe logging cable 11. The well logging cable, it should be understood,must have considerable structural strength in order to support therelatively heavy logging sonde 12, as Well as several thousand feet ofits own length.

In order for the cable to be sufiiciently small in diameter to allow forease in handling in field operation as well as the strengthrequirements, the power and frequency characteristics must be sacrificedfor the strength and handling requirements. In practice the electricalpower is restricted to the order of about 150 watts at not over about200 volts. Accordingly, when it is desired to be able to handle andtransmit information representing individual 'y ray quanta, it has beenfound diificult to transmit a sufficient amount and quantity of datacorresponding to a large number of channels of pulses of widely varyingmagnitudes to the earths surface so that a useful record may be madesimultaneous with the running of the logging sonde 12 in the well bore13. This is due primarily to the fact that these pulses are each of suchshort duration and follow in such rapid succession that a high-frequencytransmission system would be required even when the total amount ofinformation i limited.

In accordance with the present invention and the aforementionedcopending applications, there is provided an improved system for storinga complete spectrum, representing as many as 200 channels of 'y rayenergies of varying magnitude pulses in which each of the pulses isstored as an electrostatic charge on a storage surface 14, of acathode-ray tube storage tube 15. It should be noted that the schematicrepresentation of the cathode-ray storage tube in the drawings of thisapplication indicates only those elements having a function in theperformance of the method of this application and, in this respect,should be considered as merely illustrative of the form the tube mayactually take. The storage and readout portions are not separatelyillustrated but it should be understood that the readout operations mayincorporate additional elements within the tube and may function as asecondary emission collector instead of the simplified form as shown.

In the embodiment of the invention illustrated in FIG. 1, the 7 rayquanta to be stored on the storage surface 14 of the cathode-ray tube 15arise from neutron bombardment of the earths formation, such as 21, byneutrons from source 22, which are captured by nuclei of constituentelements Within the formation 21.

The neutron source 22, which may be a polonium beryllium source to givehigh neutron and low 'y ray production, is embedded wti'hin a shield 23,such as bismuth to reduce the number of 'y rays entering the formation,and further to reduce the number of 'y rays of low energy returning fromthe formation. The individual neutron capture 'y ray quanta,characteristic of the individual nuclei in the formation are thendetected by a scintillation counter including a crystal 24, such assodium iodide activated by thallium and a directly coupledphoto-multiplier tube 25. The scintillation counter further includes apreamplifier 26 wherein all electrical pulses from the photo-multipliertube, as actuated by the crystal 24, are made substantially equal inlength and proportional in magnitude to each of the 7 ray quantadetected by the counter. As shown, the scintillation counter combinationof crystal 24, photomultiplier tube 25 and preamplifier 26, ispreferably enclosed Within a further shield 27 constructed of boron inorder to prevent thermalized neutrons from entering the detector andfurther enclosed within a Dewar flask 28 to prevent the extremes intemperatures encountered within the well here from causing thegeneration of random pulses in the photomultiplier tube. The electricalpulses from the scintillation counter are of exceptionally shortduration (about .25 microsec- 0nd in duration) and, when developed froma high intensity neutron source as herein disclosed, result in as manyas one million counts per second being generated in the electricalcircuit. Accordingly, for a direct transmission system of these pulsesto the surface, a band Width of at least one megacycle, and preferablymore, would be required.

The foregoing frequency requirements in view of the aforementionedlimited power and frequency characteristics of the cable 11 require thatthe electrical pulses from the scintillation counter be converted to amore usable form while still retaining informational characteristics ofeach of the 'y ray quanta detected by the counter. To accomplish thispurpose the logging sonde 12 includes further circuitry for theselection and conversion of the short duration electrical pulses intomore easily handled waveforms for transmission to the earths surfacewith a minimum amount of modification before application to the storagesurface 14 of the cathode-ray storage tube 15. This circuitry includes adiscriminator 29, a gate generator 30 and a pulse stretcher 31 fed fromthe preamplifier 26 wherein the electrical pulse from the scintillationcounter is converted from a sharp pulse to a stretched rectangular pulseproportional in amplitude to the ampltiude of the input pulses. TheOutput of the pulse stretcher 31 is fed to an amplitude comparator 32where the rectangular waveform is compared to a linear sawtooth voltagedeveloped in linear sweep generator 33 to produce a pulse signal havinga time of initiation determined by the amplitude of the electricalsignal and, in that manner, the energy of the 'y ray detected. Theoutput of the amplitude comparator is fed to a rectangular gategenerator 34 of conventional bi-stable multivibrator design which isthereby returned to its normally Off state having been previously turnedOn by a trigger pulse from the pulse stretcher; a pulse is thus formedhaving its duration or width determined by the energy level of the 'yrays detected by the scintillation counter. The particulars ofconstruction and operation of the foregoing down hole components of thelogging tool of the present invention will be more fully explainedhereinafter along with the interconnection and coordination of each withthe other.

The output of the rectangular gate generator 34 will be transmittedalong the cable 11 to the components of the logging tool located at theearths surface. The outs put of the rectangular gate generator will be arectangular Waveform having a time duration proportional to the energylevel of the 'y ray detected, and, as such, may be used to developenergizations for the storage tube 15. The storage tube 15 is providedwith a rotating magnetic deflection coil 41- and a motor 42 is providedfor rotating the deflection coil around the electron beam of the storagetube at a constant speed. The individual bits of information derivedfrom-the energy of they rays detected by the scintillation counter willbe stored on the surface 14 of the storage. tube 15 as. discrete tracesas shown in FIG. 2 with the radial. distance of. these traces from thecenter of the storage surface proportional to the energy of the 'y raysdetected. To accomplish this proportionality the rectangular waveformoutput of the rectangular gate generator 34. transmitted along cable 11to the components of the logging tool at the. earths surfaceis fed to apulse shaper 43 such as thewell-known Schmitt trigger circuit where itis reformed for: energization of the actuating circuits for-the storagetube 15. The pulse shaper 43 provides a pair. of outputs constituting arectangular waveform. being fed to a linear sweep generator 44 forinitiation of the radial sweepto be, applied to the rotating deflectioncoil and the sharp pulse output of the trigger circuit 4-3 being fed toa pulse generator 45 to. develop .a gating pulse for controlling theelectron beam.

of the storage tube 15. Through the application of a linear sweepcurrent derived from the sweep voltage to the deflection coils 41 of thestorage tube and the sharp pulse gate. from the pulse generator 45 tothe electron control elements of the storage tube the informationrelated to the detected 'y ray will be positioned on the storage surface14. of they storage tube 15 in the form of discrete traces 46 radiallydisposed from the center of the storage surface. a distance proportionalto the energy of the 'y ray detected. Asa preferred manner of operation,the radial deflection of the electron beam of tube 15 is such. that thelow energy y rays will be represented by traces near the outer peripheryof the storage surface 14.

correspondingly, the higher energy traces will be posi-.

tioned nearer the center of the target surface.

In the form herein specifically shown, this is accomplished in the downhole. circuitry wherein the minimum original pulse amplitude, results ina pulse width for transmission through the logging cable. This timemodulation is stated by the following expression:

At: T-ke where At=rtime duration of the time modulated pulseT=predetermined maximum time for analysis of pulses of the lowest signallevel.

k =3. proportionality factor e=the energy of the 'y ray In analternative form, not herein specifically shown, the time modulation ofthe transmitted signal may take the form expressed as:

At: Ice

with the symbols having the same meanings as above. The informationtransmitted in the form of Equation 2 is ultimately converted at theearths surface to the form of Equation 1 for application to the storagetube.

The above arrangement for distributing the traces has a particularadvantage in the recording of neutron capture 'y rays where the veryhigh energy pays, i.e., upwards of 7- mev., are of much lower incidencestatistically when compared to the 'y ray energies of about 1 rnev., theratio being about 1000:l. Thus, it will be seen that utilizing therelatively large circumferential area around the outer periphery for thelow energy y ray pulse storage will permit more effective use of thearea of the storage target 14.

The storage tube 15 is ofconventional construction and is provided withelectrically actuatable elements forreading out the information storedon the storage surface 14 thereof. The energization of the readoutelements of the storage tube 15 is more fully explained in theaforementioned copending applications with reference herein to itsoperation being merely that the information stored on the storagesurface 14 may be converted to electrical signals for energization of areadout amplifier and recorder. A read and write control switch isprovided at 47 for disconnecting the electron beam circuit of thestorage tube 15 from the pulse actuating elements 45 and for connectingit to a DC. bias voltage. A pulse counter 49 is provided to be actuatedby the pulse generator 45 and, as has been hereinbefore indicated, theread and Write control switch 47 may be either automatically operated bythe pulse counter to provide a readout arrangement after a predeterminednumber of pulses have been stored on the storage tube or the read andwrite control switch may be manually operated to perform the samefunction. The readout amplifier 4%} drives a readout recorder 51 having,as shown in FIG. 2, a stylus 5-2 for indicating on a record paper 53 theinformation stored on the storage surface 14. The record paper 53 ispreferably driven by a constant speed motor 54.

A depth indicator 55 mechanically driven by the cable reeling mechanismsprovides an output to the readout recorder 51 for indication on therecord 53 of the location within the Wfill bore of the 'y ray spectrabeing recorded.

The readout of the information stored on the surface 14 of tube 15 isaccomplished in the manner defined in my aforementioned copendingapplication. In that application the electron beam is deflected by meansof electrostatic deflection plates whereas in this application theelectron beam is deflected by electromagnetic deflection coils with thecoils rotating around the electron beam to provide the circular patternof stored information as illustrated on the storage surface of thestorage tube in FIG. 2. Readout is accomplished by deflecting anelectron beam from the same electron gun in a spiral path starting fromthe exterior of the storage surface 14 and moving in a gradual spiraltoward the center thereof. As an alternative the spiral sweep mayoriginate at the center of the storage surface and move outward to theperiphery.

In writing on the storage surface of the storage tube, the sweepgenerator 44 is actuated to produce a linear sawtooth sweep having aduration sufficient to deflect the electron beam across the radialdimension of the storage surface so that the electron beam of thestorage tube 15 is deflected toward the periphery of the storage surface14. The deflection coils 41 are continuously rotated around the electronbeam by means of the motor 42 so as to effect a random positioning ofthe electrostatic charge modification of the storage surface 14 at theradial distance corresponding to the desired 'y ray energy.

In FIG. 2 is illustrated a switching arrangement for connecting thecathode-ray tube 15 for both reading and writing. The read and writecontrol switch 47 is indicated as controlling the energization of asolenoid 61 by a bat te ry 62, having mechanical connections with aplurality of switches 63, 64 and 65. In the position of the circuit asshown in FIG. 2 the storage tube 15 is connected for writing operation.With the solenoid 6-1 energized each of switches 63, 64 and 65 will bemoved in an upward direction, as viewed in FIG. 2, to connect theswitches to the other of the contacts shown; switch 63 is operative toenergize the drive motor 54 for the recorder 51, switch 64 removes thesawtooth sweep from generator 44 for the deflection coil and connectsthe sweep generator 66 generating the aforementioned spiral sweepwaveform, and switch 65 disconnects the electron beam control portionsof the storage tube 15 from the pulse generator 45 and connects it to aD.=C. bias voltage to energize the storage tube for its readoutoperation.

The circuits for converting the output of the scintillation counter frompulses of high frequency and short duration will now be described. Ashas been previously explained the cable 11 is incapable of handling thepulses in the form derived from the scintillation counter necessitatingthe conversion of these pulses to a more usable form. The circuitdiagrams of FIGS. 4 and 5 illustrate the pulse stretcher and amplitudecomparator circuits for converting the scintillation counter output froma pulse having an amplitude proportional to the energy of the 'y ray itrepresents to a pulse having a time duration proportional to theamplitude of the detected 7 ray.

The output pulse of the preamplifier 26 passing through thediscriminator 29 is fed to the pulse stretcher circuit including adifference amplifier circuit 71 comprising a pair of vacuum tubes 72 and73. The pulse, with its amplitude proportional to the energy of the 7ray detected, is applied to the control grid 74 of tube 72 and afeedback signal is applied to the control grid 75 of tube 73 derivedfrom a source to be explained hereinafter. The anode 76 of tube 72 isconnected by conductor 77 to the control grid 78 of a vacuum tube 79 ofa two-tube series amplifier 81 having as the second stage a vacuum tube82, the anode 83 of tube 73 being connected by a conductor 84 to thecontrol grid 85 of the tube 82. Conduction through tubes 72 and 73 iscontrolled by constant current device tube 80 such that the totalcurrent through the two tubes remains constant to be proportionedbetween the two tubes. The cathode 86 of tube 82 is connected to anegative potential source at conductor 87 and the anode 88 is connectedto the cathode 89 of tube 79. Anode 91 of tube 79 is connected through asuitable voltage dropping resistor 92 to a source of positive potentialat conductor 93. The junction of anode 88 of tube 82 and cathode 89 oftube 79 is connected by conductor 94- to the cathode 95 of a vacuum tube96 of the secondary emission type. Tube 96 has an anode 97, a dynode 98,a control grid 99 and other conventional elements usual with a tube ofthe type shown. The cathode 95 of tube 96 is connected through a loadresistor 100 to the anode 181 of a tube 102 having its cathode 103connected through circuit means to the negative potential at conductor87. Control grid 104, of tube 102 has applied thereto, through acoupling capacitor 105, a gating pulse from a source to be describedhereinafter, and an adjustable DC. bias from potentiometer 112 seriallyconnected with resistor 111 to provide a voltage divider networkconnected between ground and the conductor 87.

The dynode 98 of tube 96 is connected to one side of a capacitor 106 andto the anode 107 of a tube 108 the cathode 109 of which is connected tothe other side of the capacitor 106 and through circuit means to ground.The control grid 113 of tube 108 has a gating pulse applied thereto froma source, to be later described, through a coupling capacitor 114 and isfurther connected by circuit means to a source of potential positivewith respect to the cathode 109. The anode 107 is directly connected tothe control grid 115 of a vacuum tube '116 operating in acathode-follower circuit with its anode 117 connected to the positivesource at conductor 93 and its cathode 118 connected through loadresistors 119 and 121 to ground. The junction of resistors 119 and 121is connected by conductor 122 to the control grid 75 of the tube 73applying the previously defined feed back to that tube.

Referring again to tube 96, its anode 97 is connected through theprimary 123 of a transformer 124 to the positive potential at conductor93. The secondary 125 of the transformer is connected through circuitmeans to the cathode 126 and control grid 127 of a vacuum tube 128operating as a so-called bootstrap cathode follower amplifier with thecathode 126 connected through load elements 129 to ground and the anode131 connected to the positive potential at conductor 93. Cathode 126 isalso directly coupled to the control grid 132 of a vacuum tube 133operating as a cathode follower and having its cathode 134 connectedthrough load means to ground and 8 its anode 135 connected to thepositive potential at conductor 93. A load resistor 136 is provided inthe cathode circuit and a coupling capacitor 137 is connected to pickoff this pulse for triggering the time modulated pulse generator 34 aswill be more fully described hereinafter.

The circuit elements just described constitute a pulse stretcher for thepulse height analyzer and operate in the following manner:

Pulse stretching is accomplished by charging capacitor 106 to a positivepotential with current flowing through the dynode 98 of tube 96; theeventual charge is made proportional to the peak value of the inputpulse to tube 72 by means of the feedback circuit through conductor 122.

With no input signal, the capacitor 106 is kept discharged by thenormally conducting tube 108. Tube 108 is driven into cut-off before aninput pulse to the capacitor 106 reaches its maximum height by anegative gating pulse through coupling capacitor 114 derived from theinput discriminator circuit 29 and gate generator 30 fed through thepreamplifier 26. In this manner the pulse stretcher circuit provides anoutput only with input signals of a predetermined voltage level.

Tube 96 is biased at, or close to, cut-off by the voltage drop acrossthe load resistor of tube 102 in its cathode circuit with the controlgrid 99 connected to be negative with respect to the cathode 95. Thecathode potential of tube 96 is adjusted by variable resistor 110, inthe control grid circuit of tube 79, such that the steady statecathode-dynode potential results in an electron secondary emission ratioof the dynode in tube 96 near unity. This control of the cathodepotential is accomplished by the D.C. coupling of the grid 78 of tube 79to the anode of tube 72 through a voltage divider network includingvariable resistor 110. Adjustment of resistor will change the D.C.voltage on grid 78 and, because tube 79 is essentially a cathodefollower, the cathode 89 will move with the grid 78. The cathode 95 oftube 96, being directly connected to cathode 89 of tube 79 will be movedto the same adjusted potential. In the fore-going manner the potentialdifference between the dynode 98 and the cathode 95 is adjusted tomaintain the electron secondary emission ratio of the dynode near unityor a net dynode current of zero. The current through tubes 79 and 82controls the potential on the cathode 103 of tube 104 and this, alongwith the gridbias potentiometer 112, controls the conduction throughthat tube and therefore the grid-cathode voltage of tube 96.

When an input pulse appears at control grid 74 of tube 72, the amplifiedsignal is applied push-pull to the two tube series amplifier tubes 79and 82. The amplified signal through tube 72 is fed to the control grid78 of tube 79 and the amplified signal through tube 73 is fed to thecontrol grid 85 of tube 82. The initial amplified signal from tube 72drives the grid 78 of tube 79 negative toward cut-01f thus reducingcurrent flow through tube 79 and allowing cathode 89 to move negatively.At this time tube 82 is caused to conduct more heavily by the positivesignal on grid 85. Current flow through tube 82 then passes through tube96 because of the conduction condition of tube 79. The heavier currentthrough tube 82 increases the voltage drop across the resistor in thecommon cathode circuit of tube 82 and tube 102; thus effectively cuttingoff tube 102 and further decreasing the current through tube 79 thusreducing the negative bias between grid 99 and cathode 95 of tube 96.The cathode 95 of tube 96 is now sufficiently negative with respect tothe dynode 98 that the flow of electrons through the tube causes asecondary emission ratio greater than unity and a net electron currentwill leave the dynode and be accelerated through tube 96 to the anode97. These electrons are available to the dynode 98 from the capacitor106 and thus a rapid charging of capacitor 106 is effected. The chargeon capacitor l06 and-the potential of the dynode 98 permits increasedcurrent flow through tube 116 causing a positively increasing'voltagetoappear across the load resistors 119 and 121 in the'cathode circuitthereof. This positively increasingvoltage is fed back by conductor 122to=the control grid 75 of tube 73to increase the current fiowthroughthis'tube and, because of the constant current control oftube; 80,-decrease the cur-rent through tube" 72; The increase in current throughthe load resistor in the anode circuit of tube 73 decreases the voltageat g1id-85 of tube 82causing a decrease of current through tube 82" andresistor 120, allowing tube 102 to beginto conduct again. At the sametime, the decrease in'currentthrough tube 72* allows the grid 78 of tube79to'become more positiveto permit increased current aflow through thetube- 79-and causecathode 89 to return tea more positive condition; thisincreased current in tube-79 and the increased current through tube 102changes the bias between cathode 95 and grid 99 of tube 96" to returnthegrid'99 to a-controlling potential.

Theabovevoltage movements of the various elements of tubes--72, 73, 79,82, 102 and 116 areeffected extremely rapidly thus= givingcapacitor 106a very rapid charge" and a sharp rise to the waveform as shown adjacentto tube 116. Capacitor 106 continues to change until thevoltage fed backby conductor 22 to grid 75 of tube 73 equals the input signal voltage togrid 74 of tube 72 at which timethere will no longer be an error signalbetween tubes 72 and 73 and therefore no error signal to thetube'79 and82 to keep tube 96 conducting as above. Capacitor 106 will remaincharged until the gating pulse from gate generator 30 through capacitor114 is removed-from the grid 11=3 and during this period tube 11'6'willcontinue to conduct to produce a stretched pulse having an amplitudeproportional to the amplitude of theinput signal from the preamplifier26. When tube 1-08 is gated into conduction, capacitor 106 will berapidly discharged and tube 116 will terminate its conduction.

The termination of current flow through tube 96 when there is no errortotubes 72 and 73 initiates a pulse in the secondary 125 of transformer124 for application between the grid 127 and the cathode 126 of tube128. The output of tube 128 is fed'to cathode follower tube 133 toprovide al ow impedance pulse for triggering On the time modulated pulsegenerator through capacitor 137. Thepositive rectangular waveform outputof the time modulated pulse generator, as hereinafter defined, is fed tothe control grid 104 of tube 102 through coupling capacitor 105 causinga surge of current through tube 102 to prevent the pulse stretcher frombecoming responsive to a second input signal during the period it isdeveloping a pulse in response to an input signal from thepre-amplifier' 26.

The output stretched pulse from the signal indications derived throughthe circuits of FIG. 4 is fed to the amplitude comparator circuit 32 forcomparison to a linear sweep signal from sweep generator 33. In thecomparator circuit a signal is produced having a time of initiation,relative to the sweep start, determined by the energy of the 'y ray ofthe original signal indication from which the stretched pulse wasproduced. The amplitude comparator circuit 32 constitutes adiscriminator 141 including vacuum tubes 142, 143 and 144 with tube 144operating as a constant current device for tubes 142 and 143. Thestretched pulse output from tube 116 of FIG. 4 is fed to the controlgrid 145 of tube 143 and a linearly decreasing sawtooth type sweep isfed to grid 146 of tube 142 from sweep generator 33. The anodes 147 and143- of tubes 142 and 143, respectively, are connected through equalload resistors to the source of positive potential at conductor 95 and apair of equal series resistors 149 and 151 interconnect the two anodes.At the junction of the two resistors a feedback signal is picked offthrough capacitor 152 and fed to the control grid 153 of tube 144 toprovide a negative feedback helping to keep the reference value of theoutput signal constant, as will be seen hereinafter. The control grid153 is biased to a desired constant current operating condition by theunbypassed resistor in the cathode circuit and the voltage dividernetwork of resistor 154 and 155. Further stabilization of the referencevalue of the output signal is provided by the capacitor coupling thescreen grids and cathodes of both tubes 142 and 143.

A pair of diodes 156 and 157 are connected in series with their anodesback-to-back, between the junction of the resistors 149 and 151 and theanode 148 of tube 143 so that the signal output of the discriminatorcircuit may be picked off at the junction of the two diodes by conductor158.

The output of the discriminator circuit is applied through conductor 153to a differentiating circuit comprising capacitor 159 and resistor 161shunted by diode 162. The differentiated signal is applied to thecontrol grid 163 of vacuum tube 164 operating as a conventionalamplifier stage having its amplified output fed to additional amplifyingstages in tubes 165 and 166 operating as cathode-coupled amplifiers. Theoutput of tube 166 is fed through a differentiating circuit of couplingcapacitor 16 7 and resistor 163 for triggering Off the time modulatedpulse generator 34 as will be more fully described hereinafter.

The operation of the foregoing circuits is as follows: The control grids145 and 146 of tubes 143 and 144, respectively, are biased such as thatin a quiescent condition tube 142 is conducting heavily causing tube 143to be cut off, this because of the lower positive potential on grid 145and the constant current control of tube 144. The quiescent currentthrough tube 144 is determined by resistor 150 and the biasing voltagedivider network of resistors 154 and 155. The baseline of the negativegoing sawtoothed sweep input to tube 142, as shown adjacent to the grid146 from the sweep generator 33 of conventional design, is more positivethan the positive peak of a stretched pulse input to tube 143, as shownadjacent to grid 145, from the previously described pulse stretcher 31,so that tube 143 cannot conduct until the sweep on grid 146 of tube 142has reduced this grid voltage to within about 5 volts of the voltage ongrid 145 of tube 143. When the voltage on the two grids becomesubstantially equal both tubes will conduct and there will besubstantially no difference voltage between the anodes 148 and 147 ofthe two tubes and therefore no signal out-put. Before this condition ofsubstantial equality between grid voltage and when tube 143 is cut ofi,the cathodes of tubes 142 and 143 are following the negatively goingsweep on the grid 146 and the voltage at the junction of the tworesistors 149 and 151 remains substantially constant as do the voltagesat the anodes of tubes 1'42 and 143; this is the result of the action ofthe constant current tube 144 and the maintenance of a constantscreen-cathode potential for tubes 142 and 143 by the screen-cathodecoupling capacitor 160.

Any variation in the reference voltage at the junction of the tworesistors 149 and 151 is applied to the grid of the constant currenttube 144 in a manner such that as the sweep signal on grid 146 movesnegatively the bias on tube 144 is changed so as to maintainsubstantially constant the current therethrough, thus maintaining thereference point voltage substantially constant. The potential at thejunction of the two diodes 156 and 157 will be held effectively at thereference junction voltage until the signals on grids 145 and 146 causethe voltages at anodes 148 and 147, respectively, to become equal. Withthe anode 148 potential positive relative to the reference junctionpoint, the forward resistance of diode 156 is very small relative to theback resistance of diode 157 and the voltage drop across diode 156* isvery low compared to that across diode 157. When tube 143 begins toconduct, as the signals on grids 145 and 146 become nearly equal, thecurrent through its load resistor will result in the anode voltagemoving in a less positive direction while the simultaneous decrease ofcurrent through tube 142 and its load resistor will result in the anodevoltage of tube 142 moving in a more positive direction; the centralreference voltage at the junction of resistors 149 and 151 is thereforeheld constant. At the instant the anode voltage of tube 143 swingsnegative with respect to the reference junction voltage, when thepotentials on grids 145 and 146 are substantially equal, the relativeresistances of diodes 156 and 157 will reverse, and the potential attheir junction will move with that of the anode 148 of tube 143. Thevoltage at anode 148, and at the diode junction, continues to swingrapidly negative with the sawtooth signal until tube 142 is cut off andtube 143 conducts fully. The anode potentials remain at these new levelsuntil the signals are removed from the two grids 145 and 146. Theresulting negative step signal from the diode junction is differentiatedby capacitor 159 and resistor 161 and applied to control grid 163 oftube 164.

The signal to the grid 163 will be a single ended negative pulse throughthe provision of the bypass diode 162 and the diodes 156 and 157 whichallow for the rapid removal of the charge on capacitor 159 and for a lowresistance path around the resistor 161 across which the signal for grid163 is developed.

The output of tube 164 is applied to the grid of tube 165 in theconventional manner. Tubes 165 and 166 constitute a cathode-coupledclipper-limiter amplifier with the clipped signal taken from the cathodecircuit of the tube 165 being applied to the cathode of the groundedgrid amplifier tube 166. The amplified and limited output of tube 166 istaken from the anode circuit and difierentiated through couplingcapacitor 167 and resistor 168 to produce a sharp positive pulse for thetriggering Off function in the time modulated pulse generator.

The time modulated pulse generator 34 is a conventional bi-stablemultivibrator circuit for generating a rectangular pulse output having atime duration determined by the triggers from the pulse stretcher andthe amplitude comparator. The discriminator circuit 29 selects theelectrical pulses produced by the photo-multiplier tube 25 fallingwithin a predetermined energy range thus providing an initial screeningagainst undesired low energy information. A trigger output of thediscriminator 29 initiates the operation of a bi-stable multivibratorcircuit of the gate generator 30 to activate the pulse stretcher 31. Theselected pulses from the discriminator 29 are fed to the pulse stretcher31 for widening while retaining their relative amplitudes.

The widened pulses from the pulse stretcher 31 are then fed to theamplitude comparator 32. Another output of the pulse stretcher 31, aspreviously described, is used for triggering On the time modulated pulsegenerator. The output of time modulated pulse generator, in addition tobeing fed up the logging cable 11, actuates the sweep generator 33 andenergizes a blocking circuit in the pulse stretcher 31 to eliminateinterference from other signals during a period that a selected pulse isbeing stretched. The linear sweep generator generates a negative-goinglinear sawtooth waveform which is the other input to the amplitudecomparator 32.

The output of the amplitude comparator 32 is a pulse signal indicatingthe instant of equality of the stretched pulse 31 and the sawtoothwaveform. This output is fed to the time modulated pulse generator 34 toterminate or trigger Off the aforementioned rectangular pulse.Connections are provided, as shown in FIG. 1, between the rectangulargate generator 34, the linear sweep generator 33 and the pulse-stretcher31 so that, upon termination of the rectangular pulse from the gategenerator 34, the pulse-stretcher 31 will be prepared to handle asubsequent signal from the preamplifier 26 and the linear sweepgenerator 33 will be prepared to initiate a new sawtooth waveform.

The operation of the apparatus of the present invention should bereadily apparent in view of the foregoing descriptions. The detectedindividual neutron-generated 'y ray quanta produced by the radiationfrom the neutron source 22 in its bombardment of the constituentelements of the formation 21 are converted into electrical pulses by thecrystal 24 and photo-multiplier tube 25 and amplified by thepre-amplifier 26. The discriminator 29 and gate generator 30 energizethe pulse-stretcher 31, as above described. The outputs of thepulse-stretcher 31 and the linear sweep generator 33 actuate theamplitude comparator 32 to develop a pulse indicating the equalitybetween a signal proportional in amplitude to the scintillationsdetected and a linear sweep voltage. The output of the amplitudecomparator 32 along with the output pulse from the discriminator 29trigger the time modulated pulse generator 34 to produce a pulse havinga predetermined amplitude and a time duration proportional to the energyof the neutron induced 'y ray quanta detected by the crystal 24. Thispulse, as distinguished from the low-powered, high frequency signal fromthe preamplifier 26 is fed along the cable 11 to the components of thenuclear spectroscopy apparatus of the present invention at the earthssurface, and, as shown in FIG. 1, will be received by these componentsin the somewhat degraded form as an input to the pulse shaper 43. Theindications of t and t on this input waveform are the importantcharacteristics of the transmitted waveform and will require sharpeningin the pulse shaper 43 to produce the sharpened rectangular waveformoutput as illustrated. The differentiated output of the pulse shaper 43that is coincident with the trailing edge of the rectanguar waveform att actuates the pulse generator to produce a sharp pulse of very shortduration. The rectangular waveform output actuates the linear sweepgenerator 44 for the storage tube 15. The output of the pulse generator45 is fed to the electron control portions of the storage tube 15 toenergize the storage tube at the time predetermined by the downholecomponents of the nuclear spectroscopy apparatus. The linear sweepgenerator output is fed to the magnetic deflection coils 41 afterconversion from a voltage waveform to a current waveform to produce thedesired deflection of the electron beam for positioning the traces asshown in FIG. 2 at 46. It should be apparent that the electron gun isactuated to cause charge modifications of the storage surface 14 incircular paths about the center of the storage surface 14 in accordancewith the energy of the 'y ray quanta detected.

At this point in the operation of the present invention the individual'y ray quantum detected by the downhole components of the apparatus arepositioned upon the storage surface 14 as radially disposedcharge-modified portions of the storage surface in accordance with theenergy of the determination of the constituent elements of the earthsformation 21. Upon actuation of the readwrite control switch 47, eitherafter a predetermined number of pulses or after a predetermined timeperiod, the storage tube 15 will be switched from its write operation toa read operation wherein the information stored as electrostatic chargemodified portions of the storage surface 14 is readout for recording.The readout, as has been described, is preferably accomplished bydeflecting the electron beam of the storage tube 15 in a spiral pathfrom the periphery of the storage surface in a gradually decreasingmanner towards the center of the storage surface either in a 'linearpath or in gradual steps producing a series of circular traces each of areduced diameter of a predetermined increment. The signal produced uponreadout scanning of the storage surface 14 and optionally filtered toimprove the signal to noise ratio, is amplified by readout amplifier 48to be fed to the readout recorder 51 along with an indication from thedepth indicator 55 of the position of the sonde 12 Within the well bore13 13. The recorder 51 drives a stylus 52 to produce the indication onthe record paper 53 of a nuclear spectroscopy graph of conventionalformation whereby those familiar with the art may determine theconstituent elements of the well bore constituting the earth formation21. p

In FIG. 3 is illustrated a continuously operable nuclear spectroscopysystem for recording nuclear energy spectra of a well bore or the like.Like components of this circuit and the apparatus of the foregoingdescription are designated by the same reference numerals withsubscripts a and b to associate the elements with their respectivesections. As shown in the drawing, the sonde i2 incorporating thedownhole components of the nuclear spectroscopy system is supported on acable 11 transmitting its signal to the pulse shaper 43 and pulsegenerator 45. The output of the pulse generator 45 is fed selectively toeither of two complete recording units through a multi-blade switch 2%having an operating handle 201 and including double pole, double throwswitching elements 202 through 2%. Each of the recording sectionsinclude a cathode-ray storage tube, 15a and 15b with magnetic deflectioncoils 41a and 41b and storage surfaces Ma and 14b. A single fast sweepgenerator 44- is provided for writing and a pair of video amplifiers 48aand 48b are provided for readout and monitoring.

A monitoring cathode-ray oscilloscope 211 is provided for viewing theinformation being stored in a readout of the storage tubes 15a and 15band a rotating magnetic deflection coil 212 is provided for the monitorscope. A single slow sweep generator 66 is provided for the readoutsweep drive to the magnetic deflection coils 41a, 41b and 212 and thefast sweep generator 44- is connectable to the deflection coil 2-12 forthe writing sweep thereon. It should be understood that a common drivemotor may be provided for all of the rotating magnetic deflection coilsor each may be driven separately. The common drive being preferred inView of the synchronization it would provide.

The continuous nuclear spectroscopy system of this figure includes arecorder 51 and a depth indicator 55 for actuating the stylus S2 forrecording on the record chart 53 driven by the motor '54.

The operation of the continuous system is such that while one section ofthe system is operating as a storage circuit the information previouslystored in the other sections may be read out and recorded in the mannerpreviously defined with respect to FIGS. 2 and 3. The monitoroscilloscope 2.11 may be connected either to view the information beingread from one of the sections or to indicate the information beingstored in one of the sections by the operation of a monitor switch 214-.

With switch 206 in the position as shown in FIG. 3 section b of theapparatus will be actuated for writing and the storage "of nuclearspectroscopy information on the storage surface 14b of storage 15b.Switch 262 will connect the output of the pulse generator 45 to electrongenerating elements of the proper storage tube for storage operation andswitch 203 will connect the electron generating elements of the otherstorage tube for reading operation. Switches 2%, and 205, at the sametime select the proper sweep for the respective operations. Switch 2%will connect the proper video amplifier 4811 or 4% to the recorder 51through the filter circuits if desired. \Vhile switch 2th} has connectedthe components of the b circuit for writing and the components of the acircuit for reading, the conductors of FIG. 3 have connected to themonitor switch 234 the proper sweeps and signals to permit that switchto select the desired patterns for viewing. With switch 214 in theposition shown the monitor oscilloscope 2L1 will be actuated by thesignals being stored on tube 15b as passed through the video amplifier43b and the deflection coil 212 will be energized by the fast sweep 44.With the switch 214 in its a position, the oscilloscope will be actuatedby the signals being read 14 from the storage tube 15a through videoamplifier 48a and the deflection coil 212 will be energized by the slowsweep 66.

The reversal of switch 200 will reverse the conditions of sections aand'b and will change the energization of the monitor oscilloscope 211in accordance with the changes effected by the operation of the masterswitch.

The foregoing descriptive matter has illustrated the use of the presentinvention in one preferred mode of operation as a well logging tool fordetermining the constituent elements along a well bore or the like. Theinvention should not be restricted to the particular grouping or splitof the apparatus illustrated in that the invention is equally applicableto' well logging systems having all the detecting and recordingapparatus down-hole within a sonde as well as to a system having onlythe initial scintillation pulse producing sections down-hole and all ofthe pulse forming, shaping and resolving sections at the earths surfacealong with the recording facilities.

The invention has additional applications in the analysis of complexwaveforms of considerably lower relative frequency in which theinformation derived from the complex waveform may be a piecing togetherof information resolved from incremental portions of the originalcomplex waveform. In that application of the invention the apparatuswill'be actuated by small portions of the waveform rather than highfrequency signals as preferred form illustrates and will perform itsduty by collecting and storing information concerning the waveform forlateranalysis and/or regrouping.

This invention has further applications in the general art of nuclearspectroscopy aside from the preferred form herein illustrated. In otherobvious applications the invention may be used to detect not only thepresence but also the amount of a selected element present in a sampleor particular location. In this respect heretofore difficult medical orspectral analyses may be readily handled to produce a display of a longduration analysis or a group of shonter period analyses.

It should be understood that while the apparatus herein disclosedspecifically illustrates cathode-ray tube storage devices employingrotating electromagnetic deflection coils, this application is not sorestricted in that the coils may be retained physically stationary anddeflecting field thereof may be caused to rotate by suitable electricalenergization. Furthermore, the operation of the circuits of thisinvention are equally applicable to cathode-ray storage tubes employingelectrostatic deflection means providing the rotating field as is hereindescribed with the electromagnetic deflection system.

The invention is not restricted to the specifically disclosed method andcircuitry for accomplishing amplitudeto-tirne conversion. Alternatively,non-linear sawtooth waveforms, such as exponential, parabolic,hyperbolic, or similar functions, may be employed instead of the linearsawtooth waveform illustrated. Also, the functions of the sweepgenerator, pulse-stretcher, amplitude-comparator and time modulator maybe combined wholly or in part, in a single circuit, as for example, thewell-known phantastron. Other pulse-stretching and/oramplitudecomparison circuits well known in the art may be substitutedfor the circuits shown.

While a certain preferred embodiment of the present invention has beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

I claim:

1. The method of storing a discrete bit of information having a distinctcharacteristic on a storage surface of a cathode ray storage tubecomprising the steps of generating a discrete pulse having a distinctamplitude representing the distinct characteristic of said bit ofinformation, stretching said discrete pulse to a predetermined timeduration while retaining said distinct amplitude, initiating a linearlysloping sawtooth waveform signal in synchronism with the initiation ofsaid stretched pulse, the maximum amplitude of said sawtooth waveformbeing at least as large as the largest distinct amplitude of saidinformation to be stored, comparing the amplitude of said stretchedpulse to the amplitude along said sawtooth waveform, generating anelectron beam within said storage tube, directing said electron beamtoward said storage surface, rotating a deflection means about saidelectron beam and energizing said deflection to sweep said beam radiallyoutwardly from the center of said storage surface in accordance with theposition of said rotating deflection means, initiating the energizationof said deflection means at the beginning of a discrete pulse, andgating said electron beam upon the occurrence of equality in amplitudebetween the stretched pulse and the sawtooth signal initiated by thesaid discrete pulse initiating said deflection means energization toproduce a portion of a trace on said storage surface at a distinctradial distance from the center of said storage surface in accordancewith said distinct characteristic of said information.

2. Apparatus for positioning information on the storage surface of acathode ray storage tube at distinct radial distances from the center ofsaid storage surface in a circular sweep pattern, said distinct radialdistances being determined in accordance with a distinct characteristicof said information, comprising:

(a) means for generating an electron beam within said storage tubeincluding means for directing said beam toward said storage surface andmeans for deflecting said beam, means for rotating said deflecting meansabout said beam, means for energizing said deflecting means to sweepsaid beam outwardly from the center of said storage surface in aplurality of radial sweep paths to form said circular sweep pattern,

(b) means for generating a plurality of discrete signal pulses varyingin amplitude in accordance with said distinct characteristic of saidinformation, means for stretching said discrete pulses to apredetermined time duration while retaining said amplitude of each pulseproportional to said distinct characteristic, means for generating arepeating plurality of linearly sloping sawtooth waveform signals ofequal time duration to said stretched pulses, means for synchronizingthe initiation of a sawtooth waveform with the initiation of each ofsaid stretched pulses to establish a sawtooth waveform with respect toeach stretched pulse, means for comparing the amplitude of each of saidstretched pulses to the increasing amplitude along the sawtooth waveformgenerated by that stretched pulse, means for generating a second signalupon occurrence of amplitude equality between said compared stretchedpulse and its respective sawtooth waveform, means for generating a timemodulated information signal initiated with the beginning of saiddiscrete signal pulses and terminating with said second signal,

(c) means for synchronizing the energization of said deflecting meanswith the beginning of said information signal to initiate an outwardradial sweep of said electron beam, and means for gating said electronbeam upon a termination of said information signal to produce a portionof a trace at a distinct radial distance from the center of said storagesurface in accordance with said distinct characteristic of saidinformation and at a position on said storage surface determined by therotated position of said deflecting means.

References Cited in the file of this patent UNITED STATES PATENTS2,444,036 Crost June 29, 1948 2,611,105 Nadir Sept. 16, 1952 2,885,596Kaufmann May 5, 1959

1. THE METHOD OF STORING A DISCRETE BIT OF INFORMATION HAVING A DISTINCTCHARACTERISTIC ON A STORAGE SURFACE OF A CATHODE RAY STORAGE TUBECOMPRISING THE STEPS OF GENERATING A DISCRETE PULSE HAVING A DISTINCTAMPLITUDE REPRESENTING THE DISTINCT CHARACTERISTIC OF SAID BIT OFINFORMATION, STRETCHING SAID DISCRETE PULSE TO A PREDETERMINED TIMEDURATION WHILE RETAINING SAID DISTINCT AMPLITUDE, INITIATING A LINEARLYSLOPING SAWTOOTH WAVEFORM SIGNAL IN SYNCHRONISM WITH THE INITIATION OFSAID STRETCHED PULSE, THE MAXIMUM AMPLITUDE OF SAID SAWTOOTH WAVEFORMBEING AT LEAST AS LARGE AS THE LARGEST DISTINCT AMPLITUDE OF SAIDINFORMATION TO BE STORED, COMPARING THE AMPLITUDE OF SAID STRETCHEDPULSE TO THE AMPLITUDE ALONG SAID SAWTOOTH WAVEFORM, GENERATING ANELECTRON BEAM WITHIN SAID STORAGE TUBE, DIRECTING SAID ELECTRON BEAMTOWARD SAID STORAGE SURFACE, ROTATING A DEFLECTION MEANS ABOUT SAIDELECTRON BEAM AND ENERGIZING SAID DEFLECTION TO SWEEP SAID BEAM RADIALLYOUTWARDLY FROM THE CENTER OF SAID STORAGE SURFACE IN ACCORDANCE WITH THEPOSITION OF SAID ROTATING DEFLECTION MEANS, INITIATING THE ENERGIZATIONOF SAID DEFLECTION MEANS AT THE BEGINNING OF A DISCRETE PULSE, AND